The Zend MM can be tweaked using ZEND_MM_MEM_TYPE and ZEND_MM_SEG_SIZE environment variables. Default values are “malloc” and “256K”. Dependent on target system you can also use “mmap_anon”, “mmap_zero” and “win32” storage managers.

The use of --append can be dangerous if you aren't 100% sure that the files that are
longer have only grown by the appending of data onto the end. You should thus use
include/exclude/filter rules to ensure that such a transfer is only affecting files
that you know to be growing via appended data.